AU2020262012A1 - Radiation-resistant inorganic material and fiber thereof - Google Patents

Abstract

[Problem] To provide an inorganic material which exhibits excellent radiation resistance and excellent melt spinnability. [Solution] An inorganic material that contains SiO

Description

DESCRIPTION RADIATION-RESISTANT INORGANIC MATERIAL AND FIBER THEREOF TECHNICAL FIELD

[0001] The present invention relates to a novel

inorganic material having excellent radiation resistance

and a fiber thereof. More particularly, the invention

relates to a radiation-resistant inorganic material having

excellent melt spinnability and a fiber thereof.

BACKGROUND ART

[0002] Due to the major earthquakes that struck East

Japan in March 2011 (Great East Japan Earthquake), nuclear

power plants were devastated, and enormous efforts and

resources have been forcibly put in for reactor

decommissioning and radioactive waste disposal.

[0003] On the other hand, after the Great East Japan

Earthquake, safety regulations for nuclear reactors have

been tightened, and as a result, many nuclear power plants

have been shut down, while the proportion of thermal power

generation is increasing. Coal is heavily used as the fuel

for thermal power generation, and a large amount of fly ash

is generated in that case. Fly ash has been traditionally

disposed of as a waste material; however, in recent years, fly ash has been increasingly utilized as a concrete admixture, and as a result, the amount of discarded fly ash has been decreasing. However, most of the uses of fly ash occur in the field of cement, and there is concern that when the demand for cement stagnates, the amount of fly ash to be disposed of may start to increase again. For this reason, development of new use applications for fly ash has become an urgent issue. Incidentally, the composition of fly ash varies depending on the composition of the raw material coal and the place of origin thereof (power plant and country).

[0004] As an example of advanced utilization of fly lash,

for example, JP H6-316815 A (hereinafter, Patent Document

1) discloses a fly ash fiber characterized by containing

% to 40% of A1 2 0 3 , 35% to 50% of SiO 2 , 15% to 35% of CaO,

3% to 12% of Fe203, and 2% to 5% of MgO. In the same

document, it is described that "the content of Fe203

contained in the fly ash fiber is 3% to 12%. It is

desirable that this content is as small as possible.

Furthermore, when the content of Fe203 increases, the

degree of coloration of the fly ash fiber increases, which

is not preferable. From these matters, a content of Fe203

of 12% or more is problematic and must be avoided" (ibid.,

paragraph [0054]).

In addition to fly ash fibers, for example, regarding mineral fibers, JP 2018-531204 A (hereinafter, Patent

Document 2) discloses a mineral fiber including A1 2 03, SiO 2

, CaO, MgO, and Fe203 as components, characterized in that

the content of Fe203 is 5% to 15%. In the same document, it

is described that "an increase in the iron content tends to

cause coloration of mineral fibers, and this increase is

not preferable for a use application in which a mineral

fiber maintains a visible state" (ibid., paragraph [00051).

Patent Document 1 and Patent Document 2 have in common

that A1 2 0 3 , SiO 2 , CaO, and Fe203 are used as essential

components, and it is described to the effect that the

content of Fe203 should be limited to a predetermined

amount or less (12% or less in Patent Document 1, and 15%

or less in Patent Document 2).

In addition to this, JP S60-231440 A (hereinafter,

Patent Document 3) and JP H10-167754 (hereinafter, Patent

Document 4) disclose a glass and a vitrified material

characterized in that the materials contain A1 2 0 3 , SiO 2 , CaO,

and Fe203 as essential components, and that the content of

each of the oxide components is in a specific range.

In addition to that, in Materials Research Bulletin,

36 (2001), 1513-1520 (hereinafter, Non-Patent Document 2),

the relationship between the content of iron oxide (Fe203)

and magnetism in a sample obtained from goethite (FeOOH)

industrial waste is described.

Meanwhile, none of Patent Documents 1, 2, 3, and 4 and

Non-Patent Document 2 mention about radiation resistance.

However, as previously mentioned, radiation-resistant

materials are inevitable for the treatment of damaged

nuclear power generation facilities and the treatment of

radiation-contaminated waste or radiation-contaminated

surplus soil or the treatment of radioactive waste.

As a radiation-resistant material, attention has been

paid to basalt fibers produced from basalt as a raw

material; however, as far as the inventor is informed,

there is no document discussing the relationship between

the composition of the basalt fibers and radiation

resistance. Meanwhile, in the Chronological Scientific

Tables (hereinafter, Non-Patent Document 1), the types and

compositions of basalt are introduced as follows (Table 1).

[00051 [Table 1]

<Type and composition basalt, source: Chronological

Scientific Tables>

Alkali Flood Oceanic Abyssal Island arc Component basalt basalt island basalt basalt basalt SiO 2 45.4 50.01 50.51 50.68 51.9 A1 2 0 3 14.7 17.08 13.45 15.6 16 Fe 2 0 3 4.1 - 1.78 - FeO 9.2 10.01 9.59 9.85 9.56 CaO 10.5 11.01 11.18 11.44 11.8 MnO - 0.14 0.17 - 0.17 MgO 7.8 7.84 7.41 7.69 6.77 TiO 2 3 1 2.63 1.49 0.8 Na 20 3 2.44 2.28 2.66 2.42 K2 0 1 0.27 0.49 0.17 0.44 P20s - 0.19 0.28 0.12 0.11 Total 98.7 99.99 99.77 99.7 100

In addition to this, in a review article for basalt

fibers (International Journal of Textile Science, 2012,

1(4): 19-28, Non-Patent Document 3), the representative

composition of basalt is described as SiO 2 : 52.8%, A1 2 0 3 :

17.5%, Fe203: 10.3%, and CaO: 8.59%.

CITATION LIST PATENT DOCUMENT

[00061 Patent Document 1: JP H6-316815 A

Patent Document 2: JP 2018-531204 A

Patent Document 3: JP S60-231440 A

Patent Document 4: JP H10-167754 A

NON-PATENT DOCUMENT

[0007] Non-Patent Document 1: Chronological Scientific

Tables, 2019 Edition (edited by National Astronomical

Observatory of Japan)

Non-Patent Document 2: Materials Research Bulletin, 36

(2001) 1513-1520

Non-Patent Document 3: International Journal of

Textile Science, 2012, 1(4): 19-28

SUMMARY OF THE INVENTION PROBLEM TO BE SOLVED BY THE INVENTION

[00081 As described above, as far as the inventor of the

present invention are informed, there has been no study conducted for the purpose of enhancing the radiation resistance of inorganic materials including SiO 2 , A1 2 0 3 , and

Fe203 as main components.

Thus, for the purpose of enhancing radiation

resistance, the present inventor worked on the improvement

of radiation resistance of an inorganic material including

SiO 2 , A1 2 0 3 , and Fe203 as main components, and particularly

on the development of a radiation-resistant inorganic

material having excellent melt spinnability.

MEANS FOR SOLVING PROBLEM

[00091 As a result, the inventor found that with regard

to an inorganic material containing SiO 2 and A1 2 0 3 as main

components, when the sum of SiO 2 and A1 2 03 is in a specific

range, the proportion occupied by A1 2 0 3 in the sum of SiO 2

and A1 2 0 3 is in a specific range, and the inorganic

material contains a specific amount of each of Fe203 and

CaO, the inorganic material has excellent radiation

resistance and excellent melt spinnability, and

consequently, the inventor finally completed a material

suitable for a part to be irradiated with radiation.

That is, the present invention is an inorganic

material suitable for a part to be irradiated with

radiation, the inorganic material including Si0 2 , A1 2 0 3 , CaO,

and Fe203 as components, wherein the respective mass percentages of the components in terms of oxide in the inorganic material are as follows: i) the total content of SiO 2 and A1 2 03 is from 40% by mass to 70% by mass; ii) the proportion (mass ratio) occupied by A1 2 0 3 in the sum of SiO 2 and A1 2 0 3 is in the range of 0.15 to 0.40; iii) the content of Fe203 is from 16% by mass to 25% by mass; and iv) the content of CaO is from 5% by mass to 30% by mass.

Hereinafter, the above-described conditions i) to iv)

may be simply described as "four requirements of the

present invention related to the composition".

A specific example of the part to be irradiated with

radiation, where the inorganic material of the present

invention is used, will be described below.

[0010] According to the present invention, no

substantial difference is observed between the component

ratio of various raw materials in a formulated mixture and

the component ratio of various raw materials in the

material obtained after melting the mixture. Therefore,

the component ratio in the formulated mixture can be

regarded as the material component ratio.

With regard to the inorganic material of the present invention, the formulating proportions of raw materials are adjusted such that the proportions of SiO 2 , A1 2 0 3 , Fe203, and CaO in the components are within the above-described ranges, and then the mixture is melted to obtain a final inorganic material.

As will be described below, when the raw materials are

formulated such that the formulating proportions are within

the above-described ranges, the raw materials are melted at

a temperature that is not excessively high, and since the

molten product is appropriately viscous, the molten product

has excellent melt spinnability. Furthermore, the

resulting inorganic material has superior radiation

resistance.

[0011] The total content of SiO 2 and A1 2 0 3 in the

inorganic material of the present invention is from 40% by

mass to 70% by mass. In the following description, SiO 2

may be abbreviated to "component S", and the content of

SiO 2 may be indicated as "[S]". Similarly, A1 2 0 3 may be

abbreviated to "component A", and the content of A1 2 0 3 may

be indicated as "[A]". When the sum of [S] and [A] is out

of the above-described range, that is, either less than 40%

by mass or more than 70% by mass, the material may have a

higher melting temperature, the molten product may have a

higher viscosity, or in contrast, the melt viscosity may

become too low, so that the melt spinnability may be deteriorated.

[0012] With regard to the inorganic material of the

present invention, it is required that the proportion

occupied by A1 2 0 3 in the sum of SiO 2 and A1 2 03 ([A]/ ([A]

+

[S])) (mass ratio) is in the range of 0.15 to 0.40. Even

from this requirement, when the proportion is out of the

above-described range, that is, either less than 0.15 or

more than 0.40, the material may have inferior melt

spinnability.

[0013] With regard to the inorganic material of the

present invention, it is required that the content of Fe203

is from 16% by mass to 25% by mass. When the content of

Fe203 is less than 16% by mass, the material has inferior

radiation resistance. On the other hand, when the content

thereof is more than 25% by mass, the molten product

becomes excessively viscous, and a thread is not likely to

be formed. Hereinafter, Fe203 may be abbreviated to

"component F", and the content of Fe203 may be indicated as

"[F]".

[0014] With regard to the inorganic material of the

present invention, it is preferable that the content of CaO

is from 5% by mass to 30% by mass. When the content of CaO

is less than 5% by mass, the melting initiation temperature

of the material becomes high, and it is not preferable from

the viewpoint of energy saving. The content of CaO is preferably 10% by mass or more. On the other hand, when the content thereof is more than 30% by mass, viscosity of the molten product is too low, and a thread is not likely to be formed. Hereinafter, CaO may be abbreviated to

"component C", and the content of CaO may be indicated as

"[C]".

[0015] On the occasion of obtaining the inorganic

material of the present invention, there are no limitations

on the raw materials as long as the proportions of SiO 2

, A1 2 0 3 , Fe203, and CaO are within the above-described ranges.

Therefore, each of the single compounds of SiO 2 , A1 2 0 3

, Fe203, and CaO may be prepared and used as starting raw

materials; however, it is preferable from the viewpoint of

the raw material cost that a silica source rich in the SiO 2

content, an alumina source rich in the A1 2 0 3 content, an

iron oxide source rich in the Fe203 content, and a calcium

oxide source rich in the CaO content are formulated to be

used as starting raw materials.

Examples of the silica source include, but are not

limited to, amorphous silica, silica sand, fumed silica,

and volcanic ash.

Examples of the alumina source include, but are not

limited to, alumina, mullite, and other minerals.

Examples of a substance that can serve as a silica

source as well as an alumina source (silica alumina source) include, but are not limited to, kaolinite, montmorillonite, feldspar, and zeolite.

Examples of the iron oxide source include, but are not

limited to, iron oxide, iron hydroxide, and iron ore.

Examples of the calcium oxide source include, but are

not limited to, calcium carbonate, calcite, dolomite, and

other minerals.

[0016] In addition to the above-described substances,

thermal power generation waste or metal refining waste can

also be effectively utilized as one of the silica source,

the alumina source, the iron oxide source, and the calcium

oxide source.

Fly ash or clinker ash can be used as the thermal

power generation waste. Since fly ash and clinker ash

abundantly include SiO 2 and A1 2 03 , these ashes are suitable

as silica alumina sources. Above all, since fly ash and

clinker ash have a low Fe203 content, it is difficult to

obtain the inorganic material of the present invention only

from those ashes. However, the inorganic material of the

present inventions can be obtained at low cost by

additionally incorporating an appropriately amount of an

iron oxide source. Meanwhile, since the Coal Gasification

Slag (CGS) produced as waste of the Integrated coal

Gasification Combined Cycle (IGCC) also has a chemical

composition that is almost equivalent to that of fly ash, the coal gasification slag can serve as a silica alumina source. Since the coal gasification slag is in the form of granules, it has an advantage of having excellent handleability.

Examples of the previously mentioned metal refining

waste include iron and steel slag and copper slag.

Since the iron and steel slag has a large CaO content,

this slag can be used as a calcium oxide source. The iron

and steel slag includes blast furnace slag, converter slag,

and reducing slag.

Since copper slag has a large Fe203 content, copper

slag can be used as an iron oxide source.

Therefore, appropriately, fly ash, clinker ash, or

coal gasification slag can be used as a silica alumina

source, copper slag can be used as an iron oxide source,

and iron and steel slag can be used as a calcium oxide

source. According to a preferred embodiment, most of the

silica alumina source, the iron oxide source, and the

calcium oxide source can be covered by industrial waste.

In addition to this, volcanic rocks represented by

basalt and andesite can also be utilized as the silica

alumina source.

[0017] With regard to the inorganic material of the

present invention, incorporation of unavoidable impurities

that are included in the raw materials is not excluded.

Examples of such impurities include MgO, Na20, K 2 0, TiO 2

, and Cr02.

[0018] Since the inorganic material of the present

invention is highly amorphous, a fiber that has been

processed by melt spinning hardly undergoes a decrease in

strength, which is attributable to delamination of a

crystal phase-amorphous phase interface, and a high

strength fiber can be obtained.

Here, the degree of amorphization, which is a measure

of amorphousness, is calculated by the following

Mathematical Formula (1) based on the X-ray diffraction

(XRD) spectrum.

Degree of amorphization (%) = [Ia/(Ic + Ia)] x 100

(1)

wherein in Formula (1), Ic represents the sum of integral

values of the scattering intensity of a crystalline peak

when the inorganic material is subjected to an X-ray

diffraction analysis; and Ia represents the sum of integral

values of the scattering intensity of an amorphous halo.

The degree of amorphization of the inorganic material

of the present invention may vary depending on the

composition of the inorganic material; however, the degree

of amorphization usually represents a value of 90% or more.

When the degree of amorphization is high, the value may

even reach 95% or more, and when the degree of amorphization is highest, the fiber is substantially formed only from an amorphous phase. Here, being substantially formed only from an amorphous phase implies that in the X ray diffraction spectrum, only amorphous halo is recognized, and a peak of the crystal phase is not recognized.

[0019] The radiation resistance of a material formed

from the inorganic material of the present invention can be

known by comparing the Vickers hardness obtained before and

after irradiation of the material with radiation. In

addition to this, evaluation of radiation resistance is

enabled also by comparing the tensile strength and the

porosity in the material obtained before and after

radiation exposure. For the measurement of the porosity in

the material, a positron annihilation method can be

employed.

EFFECT OF THE INVENTION

[0020] As compared to existing inorganic materials

including SiO 2 , A120 3 , CaO, and Fe203 as components, since

the inorganic material of the present invention is such

that the sum of SiO 2 and A120 3 , the proportion occupied by

A120 3 in the sum of SiO 2 and A120 3 , the content of Fe203, and

the content of CaO are in specific ranges, the inorganic

material has excellent radiation resistance and has

excellent melt spinnability.

BRIEF DESCRIPTION OF DRAWINGS

[0021] Fig. 1 is a schematic explanatory diagram showing

a summary of an evaluation test for melt spinnability of an

inorganic material of the present invention, together with

a magnified view of a melt-spun fiber;

Fig. 2 shows XRD spectra respectively obtained before

and after irradiation of a melt-spun fiber of an inorganic

material of Example 1 with radiation;

Fig. 3 is a diagram showing the relationship between

the iron oxide content in an inorganic material and

radiation resistance;

Fig. 4 is a diagram showing various examples of XRD

spectra of inorganic fibers of Examples and Comparative

Examples; and

Fig. 5 is a diagram showing various examples of a DTA

curve obtained by a differential thermal analysis of the

inorganic fibers of Examples and Comparative Examples.

MODE(S) FOR CARRYING OUT THE INVENTION

[0022] In the following description, the contents of the

present invention will be specifically described by way of

Test Examples.

In the following Test Examples (Examples and

Comparative Examples), the following were used as the silica source, alumina source, silica alumina source, iron oxide source, and calcium oxide source.

<Silica source>

* Silicon dioxide: Reagent (will be described as Si0 2

(reagent) in the following Tables 6 to 9)

<Alumina source>

* Aluminum oxide: Reagent (will be described as A1 2 0 3

(reagent) in the following Tables 6 to 9)

<Iron oxide source>

* Iron(III) oxide: Reagent (will be described as Fe203

(reagent) in the following Tables 6 to 9)

* Copper slag: Copper slag produced at a copper

smelter in Japan (will be described as FA(10) in the

following Table 3)

<Calcium oxide source>

* Calcium oxide: Reagent (will be described as CaO

(reagent) in the following Tables 6 to 9)

* Blast furnace slag: Blast furnace slag produced at

an ironworks in Japan (will be described as FA(13) in the

following Table 3)

* Reducing slag: Reducing slag produced at an

ironworks in Japan (will be described as FA(14) in the

following Table 3)

<Silica alumina source>

• Fly ash: 12 types of samples discharged from thermal power plants in Japan (will be described as FA(1) to FA(9) and FA(12) in the following Tables 2 and 3)

* Coal gasification slag: A sample discharged from an

integrated coal gasification combined cycle plant in Japan

(will be described as FA(11) in the following Table 3)

* Volcanic rocks: Basalt-based rocks having

specifically large iron oxide contents, collected in Akita

Prefecture and Fukui Prefecture (will be described as BA(1)

and BA(2) in the following Table 4)

[0023] The compositions of the above-described FA(1) to

FA(14), BA(1), and BA(2) are shown in Tables 2, 3, and 4.

The component analysis was based on a fluorescence X-ray

analysis method.

[0024] [Table 2]

<Fly ash composition, unit: % by mass>

Component FA(1) FA(2) FA(3) FA(4) FA(5) FA(6) Fe203 [F] 10 5 5 9 10 14

A - - - -3----[ ]--------- ------ 113---------

[A]--------2 3 --- _ -- 5----------1 8-1 _2 _ ------------- 18 ------------ 225 1_8 ----- Ca O [C---I ------- 12 7------------------------0---------------- 3----3 3----------- 3--------1 ------ 1 2-------------- 1--- Others 7 9 17 5 9 1 c5)i- n c~o

0 0

44~

U

-1 ',4

C

44)

-HH CY)

44) -Ho

co C0)

0 co 44

0f 0

(N NO I0 -1 cn 00

[0026] [Table 4]

<Volcanic rock composition, unit: % by mass>

Component BA(1) BA(2) Fe203 [F] 19 18 SiO2 [SI 46 25 A--23 [A] 11 10 CaO [C] 17 3 Others 7 44

[0027] <Preparation of powdered raw materials>

In the following Test Example, each of the silica

source, alumina source, iron oxide source, and calcium

source is finely pulverized, the sources are mixed such

that SiO 2 , A120 3 , Fe203, and CaO are included at

predetermined proportions, and the mixture is used for the

test.

[0028] <Evaluation of melt spinnability>

Furthermore, the evaluation of melt spinnability of

the formulation is based on a melt spinning test using an

electric furnace. An outline of the test is shown in Fig.

1. In Fig. 1, an electric furnace (1) has a height (H) of

cm and an outer diameter (D) of 50 cm and comprises an

opening (4) having a diameter (d) of 10 cm at the center.

On the other hand, 30 g of the formulation is introduced

into a Tammann tube (2) having an inner diameter (<) of 2.1

cm and a length of 10 cm. At the center of the bottom of

the Tammann tube (2), a hole having a diameter of 2 mm is

opened. During a melting test, the Tammann tube (2) is

retained at a predetermined position in the opening (4) of the electric furnace using a hanging rod (3).

When the formulation is melted by heating, the

formulation flows and drops from the bottom of the Tammann

tube due to its own weight and is solidified upon coming

into contact with outside air to become a fiber.

The electric furnace is heated by a predetermined

temperature increase program, and the highest attainable

temperature of the temperature inside the furnace is set to

13500C. At this time, it has been confirmed in advance

that the temperature inside the Tammann tube (molten

product) conforms to a temperature lower by almost 500C

than the temperature inside the furnace.

In the present invention, as an indicator for

evaluating melt spinnability, the state in which the molten

product flows and drops to form a thread until the

temperature inside the furnace reaches 13500C, that is, the

state in which the melting temperature of the sample is

13000C or lower, and the molten product has a melt

viscosity appropriate for forming a thread, was considered

as acceptable level. The melt behavior of the samples is

roughly classified into the following groups represented by

A to D.

<Evaluation ranking>

A: A thread is formed.

B: The molten and softened sample just appears from the bottom of the Tammann tube; however, the viscosity is so high that the sample does not drop by its own weight alone, and a thread is not formed.

C: Because melting of the sample is not initiated, or

melting occurs insufficiently, nothing comes out from the

bottom of the Tammann tube.

D: Although the sample melts, the melt viscosity of

the molten product is too low, the sample becomes liquid

droplets and just drips, and a thread is not formed.

<Heat resistance test>

An inorganic fiber formed from the material of the

present invention is even excellent in terms of heat

resistance. For the evaluation of heat resistance, a

differential thermal analysis (DTA) was performed.

[0029] [Tentative experiment]

A silica source, an alumina source, an iron oxide

source, and a calcium oxide source were appropriately

formulated, and then four kinds of samples having different

contents of SiO 2 , A1 2 0 3 , Fe203, and CaO were prepared and

used for a melt spinning test. Samples 3 and 4 satisfied

all of the requirements of the present invention described

previously; however, samples 1 and 2 do not satisfy the

requirement iii) related to the Fe203 content (Table 5)

All of the samples exhibited satisfactory melt

spinnability. The obtained fiber samples were subjected to a radiation exposure test using cobalt 60 as a radiation source under the conditions of a gamma ray irradiation dose of 50 kGy, the tensile strengths before and after irradiation were measured, and the retention rate was determined.

The results are shown in Table 5. Fig. 3 is a graph

obtained by plotting the relationship between the iron

oxide (Fe203) content in a sample and the fiber strength

retention rate after radiation exposure. From this, it is

clear that when the iron oxide (Fe203) content in the

material is 15% or more, the retention rate of the tensile

strength after radiation exposure becomes noticeably high.

(N 3 n N (LC )

( CCD

Cn)

aCD

CCD CfD

(N

rd rHN 1 0 C C(N 0

Cd

(N

-1 N riiCi 'Z1(n ( C C Lf-ir-Hi(N i K (N (n

Cd

-H

0 H co -H

if) co 0 G) H : 'U)

(- Q-4:) S0 -HH co 0 (9 rrC . 4CC) .

(D u (D

CC)

[0031] [Example 1]

30 parts by mass of FA(l) and 70 parts by mass of

BA(1) were formulated. The present sample has the same

composition as that of sample 3 used in the above-described

tentative experiment. The component ratio of the present

sample is [S] + [A]: 60% by mass, [A]/([S] + [A]): 0.20,

[F]: 16% by mass, and [C]: 17% by mass (Table 6).

As a result of the melt spinning test, a very fine

fiber (mineral fiber) having a diameter of 50 pm or less

was obtained within 5 hours after the temperature inside

the furnace reached 13500C. The obtained fiber had a

strength that was not likely to cause breakage even when

the fiber was pulled by hand. The present fiber sample was

irradiated with radiation under the following conditions.

<High radiation exposure test>

The above-described fiber sample was subjected to an

ultra-high dose radiation exposure test using a nuclear

reactor (thermal neutron reactor, BR2) installed at the Mol

Institute in Belgium. The gamma ray irradiation dose was

5.85 GGy. This irradiation dose was comparable to the

radiation dose emitted by common high-level radioactive

waste in about 1000 years.

[0032] The fiber sample after radiation exposure was

subjected to the following XRD analysis and Vickers

hardness test, together with a fiber sample that was not irradiated with radiation.

<XRD analysis>

XRD spectra of the fiber sample before and after

radiation exposure are shown in Fig. 2 (before irradiation:

left-hand side diagram, after irradiation: right-hand side

diagram, the axis of ordinate represents diffraction

intensity expressed in an arbitrary unit (a.u.)). Since

there is a possibility that the sample after radiation

exposure may emit radiation, only in that case, a dome

shaped shield cover with a limited opening was provided on

the sample stand. This is the reason why the range of the

measurement incident angle of the spectral data (Fig. 2,

right-hand side diagram) of the sample after radiation

exposure is narrowed.

In both the XRD spectra of the fiber sample before

radiation exposure and the fiber sample after radiation

exposure, only amorphous halo was observed, and a peak of

the crystal phase was not recognized. That is, it was

found that both the fiber sample before radiation exposure

and the fiber sample after radiation exposure are

substantially composed only of the amorphous phase, and the

amorphousness was maintained even after radiation exposure.

[00331 <Vickers hardness test>

The fiber sample before radiation exposure and the

fiber sample after radiation exposure were subjected to a

Vickers hardness test.

The testing instruments used were Reichert-Jung

Microduromat 4000E and Leica Telatom 3 optical microscope.

Considering that the width of the fiber samples was

approximately 20 pm, the force to be applied to sample

surface was set to 10 gF (0.098 N).

Measurement was performed at seventeen points in each

of the sample before radiation exposure and the sample

after radiation exposure, and as a result, the Vickers

2 hardness was 723 ± 24 kgF/mm before radiation exposure,

2 and 647 ± 19 kgF/mm after radiation exposure. The Vickers

hardness retention rate after irradiation was 89%, and when

it is considered that the gammy ray irradiation dose was

5.85 GGy, it can be said that the retention rate has a very

high value. Thus, the material has highly excellent

radiation resistance. For a comparison, the values of the

retention rate (89%) obtained by the present test were

plotted in Fig. 3, which was shown earlier. Although the

method for measuring the strength retention rate is

different, it is noteworthy that even if a sample having an

iron oxide content of 16% is irradiated with an ultra-high

dose of radiation, which is approximately 100,000 times the

dose employed in the previously mentioned tentative

experiment, the sample maintains a retention rate close to

% as the strength retention rate.

[0034] [Example 2]

A sample was prepared at the raw material formulation

ratio shown in Table 6 as Example 2. The component ratio

of the present sample is such that [S] + [A]: 60% by mass,

[A]/([S] + [A]): 0.25, [F]: 19% by mass, and [C]: 13% by

mass (Table 6).

As a result of a melt spinning test, the sample melted

and dropped within 5 hours after the temperature inside the

furnace reached 13500C, and a very fine fiber (mineral

fiber) having a diameter of 50 pm or less was obtained.

Similarly to Example 1, the obtained fiber sample was

substantially composed only of the amorphous phase, and

even if the fiber sample was pulled by hand, the fiber

sample did not easily break. Furthermore, the

amorphousness is retained even after radiation exposure,

and the Vickers hardness retention rate is also at the same

level as in Example 1. Thus, the present material has

highly excellent radiation resistance.

[0035] [Example 3]

A sample was prepared at the raw material formulation

ratio shown in Table 6 as Example 3. The component ratio

of the present sample is such that [S] + [A]: 56% by mass,

[A]/([S] + [A]): 0.20, [F]: 18% by mass, and [C]: 25% by

mass (Table 6).

As a result of a melt spinning test, the sample melted and dropped within 5 hours after the temperature inside the furnace reached 13500C, and a very fine fiber (mineral fiber) having a diameter of 50 pm or less was obtained.

Similarly to Example 1, the obtained fiber sample was

substantially composed only of the amorphous phase, and

even if the fiber sample was pulled by hand, the fiber

sample did not easily break. The amorphousness is retained

even after radiation exposure, and the Vickers hardness

retention rate is also at the same level as in Example 1.

Thus, the present material has highly excellent radiation

resistance.

[00361 [Comparative Example 1 to Comparative Example 8]

Samples were prepared at the raw material formulation

ratios shown in Table 6 as Comparative Examples 1 to 8.

All of them did not satisfy any one of the "four

requirements of the present invention related to the

composition".

As a result, none of the samples became fibrous within

hours after the temperature inside the furnace reached

13500C (Table 6)

0'~ ;

F - II 0 ''' x' I iR i '

0 r- (N

1 1 '

2 0A A: A-AA-AA A A-

CD (1)~~ Q0,A,~: O&0 '- A c D CDA

[00381 [Examples 4 to 11]

Fly ash FA(7) was selected as the silica alumina

source, reagents SiO 2 (S), A1 2 0 3 (A), Fe203 (F), and CaO (C)

were additionally formulated as necessary so as to satisfy

the "four requirements of the present invention related to

the composition", and tests were performed (Table 7,

Examples 4 to 11). All the samples exhibited excellent

melt spinnability. The radiation resistance was also

highly excellent as was in Example 1.

| |C|D| | |,| CD 0CD>00O ~~ | , I

CD o1|DI|-0 1 C j | | | | | |\J |o,| |

'I Io ICI 1 co Iiiici-C1 | | | | | || | |C g

0. | | | |I |IO | , I

Eo |I || -I --0 I4C| 1

01 1 1 0> | | 1> 0>1 || | C |

0 | | | | || 1 L| | |1

-1 31 1 (Co |J |) |) |) | |U| |

CD CD I I II o 2 )' [ l ' | l4LO| ' l ' I ' l | '

N o~ ~~ss | | | | ||| |> | |

Q~C | | | 4||, |O CDO lIII | d r-l Cl 0li | 4

|4- @ |0 | || | | | | o || D

| || 1~ co CC CC ,I Cn C

*~ ~ ~C 'CD C C> 'a

U :

0 m

[00391 Fly ash FA(7) was selected as the silica alumina

source, reagents SiO 2 (S), A1 2 0 3 (A), Fe203 (F), and CaO (C)

were additionally formulated, and tests were performed

(Table 8, Comparative Examples 9 to 16) All of

Comparative Examples 9 to 16 did not satisfy any one of the

"four requirements of the present invention related to the

composition".

When the value of [S] + [A] is less than the lower

limit of the requirement i), the viscosity of the molten

product is too low, and as a result, a thread cannot be

formed (Comparative Example 9) On the other hand, when

the value of [S] + [A] is more than the upper limit of the

requirement i), since the viscosity of the molten product

is too high, the molten product does not exhibit the

behavior of dropping due to gravity, which is a

prerequisite for thread formation, and a thread cannot be

formed (Comparative Example 10).

Even in a case where the value of [A]/([S] + [A]) is

less than the lower limit of the requirement ii), the

viscosity of the molten product is too low, and as a result,

a thread cannot be formed (Comparative Example 11) On the

other hand, even in a case where the value of [A]/([S] +

[A]) is more than the upper limit of the requirement ii),

since the viscosity of the molten product is too high, the

molten product does not exhibit the behavior of dropping caused by gravity, which is a prerequisite for thread formation (Comparative Example 12).

As a result of the X-ray diffraction (XRD) spectrum,

in Comparative Example 12, formation of a crystal phase was

recognized, which was considered to be attributable to an

A1203-rich phase (Fig. 4).

When the value of [F] is less than the lower limit of

the requirement iii), the radiation resistance is poor

(Comparative Example 13). On the other hand, when the

value of [F] is more than the upper limit of the

requirement iii), the viscosity of the molten product is

too low, and as a result, a thread cannot be formed

(Comparative Example 14).

When the value of [C] is less than the lower limit of

the requirement iv), the viscosity of the molten product is

too low, and as a result, a thread cannot be formed

(Comparative example 15). On the other hand, when the

value of [C] is more than the upper limit of the

requirement iv), since the viscosity of the molten product

is too high, a thread cannot be formed (Comparative Example

16).

P>

0) (N 0

CD

<-ID

rCD

O' LC) CD r-'

rdCD 0 KB

0>n In (

LfLC (D

QD 4

I- >mx

LI LI)~

CDC 0-) CD 3, c ,r z CrHC~ 3OOO ~

ID

C QCD 00 m

[0041] Next, prescriptions in which most of the silica

alumina source, the iron oxide source, and the calcium

oxide source were composed of thermal power generation

waste (fly ash and clinker ash) and metal refining waste

(iron and steel slag and copper slag), or volcanic rock,

which is a natural resource, were attempted (Table 9,

Examples 12 to 18).

All of the formulations satisfied the "four

requirements of the present invention related to the

composition" and had excellent melt spinnability. The

radiation resistance was also superior.

Ln C\] -A w 0c0 I : A

11(-A I~ I ICI I )AO 1 CD

xC C CD LC) C~l 9: A Lc)

Q4 (n

AI II.1.1IIII C

CD)

rC (N (\. a)

4- 1 U) U

>:4 4- I I)'j~W

CDSl( -A x\ (N

0A 4\ 0 l -- 5 ~~(N

4-) o -- 4-) 4-)A 4-) -l i - A U) a 0 r1

~w >GDGDCA(NAAA( w- 0rr0 Q4± IZI550

CD LI 3880 u 0 A CD u riO

[0043] Fig. 4 shows XRD spectra of a series of molten

samples.

Samples in which the value of [A]/([S] + [A]) does not

exceed the upper limit of the requirement ii) of the

present invention (Comparative Example 11 and Example 6)

are amorphous; however, in Comparative Example 12 in which

the value is more than the upper limit of the requirement

ii), formation of a crystal phase is recognized, which is

considered to be attributable to an A1203-rich phase.

Furthermore, even if the value of [F] changed to a

range near the upper limit of the requirement iii) of the

present invention, the material was amorphous (Comparative

Example 13, Examples 8 and 9, and Comparative Example 14).

Fig. 5 shows thermograms (DTA curves) obtained by a

differential thermal analysis of inorganic fibers obtained

in a series of tests.

The inorganic fibers of the present invention were

thermally stable up to about 800°C (at least a temperature

close to 700°C), and the melting temperature is 1200°C or

higher.

INDUSTRIAL APPLICABILITY

[0044] The inorganic material of the present invention

has excellent radiation resistance and can therefore be

utilized in the field of nuclear power, the field of aerospace, and the field of medicine.

When the inorganic material is used at parts to be

irradiated with radiation in the facilities, instruments,

and members used in these fields, radiation-induced

deterioration of these parts to be irradiated with

radiation can be suppressed.

Examples of the facilities, instruments, and members

in the field of nuclear power include:

• facilities, instruments, and members for nuclear

power generation;

• facilities, instruments, and members for mining and

processing uranium ores;

* facilities, instruments, and members for secondary

processing treatment of nuclear fuel (including conversion,

concentration, reconversion, molding processing, and MOX

manufacturing of the same fuel);

* facilities, instruments, and members for storage,

treatment, and retreatment of used nuclear fuel;

* facilities, instruments, and members for storage,

treatment, and disposal of radioactive waste;

* transport instruments and members for uranium ores,

secondary processing products of nuclear fuel, used nuclear

fuels, or radioactive waste; and

* other nuclear-related facilities, instruments, and

members.

More specific examples of the facilities, instruments,

and members for nuclear power generation include nuclear

reactor buildings (including research reactors and test

reactors), a nuclear reactor containment vessel, piping

inside a nuclear reactor facility, and a decommissioning

robot.

Examples of the facilities, instruments, and members

used in the field of aerospace include a space station

building, a space station, an artificial satellite, a

planetary exploration satellite, and a space suit.

Examples of the facilities, instruments, and members

used in the field of medicine include medical devices that

utilize particle beams.

Since the inorganic material of the present invention

has excellent melt spinnability, the inorganic material is

suitable for inorganic fibers for a fiber-reinforced

composite material. Furthermore, depending on the use

application, the inorganic material can be processed into

roving, chopped strands, woven fabrics, prepregs, nonwoven

fabrics, and the like. Examples of a base material

(material to be reinforced with fibers) of the above

described composite material include resins and cement. As

the resins, known thermoplastic resins and thermosetting

resins can be used.

Another example of use of the inorganic material of the present invention is the use as a material for three dimensional printing. That is, when a kneading product of a powder of the inorganic material of the present invention as well as a wax, a resin, and other carriers is used as a material for three-dimensional printing, it is possible to produce a member having excellent radiation resistance without limitations in the shape.

The above-described use examples have been given only

for the purpose of demonstrating the usefulness of the

present invention and are not intended to limit the scope

of the present invention.

EXPLANATIONS OF LETTERS OR NUMERALS

[0045] 1 ELECTRIC FURNACE

2 TAMMANN TUBE

3 HANGING ROD

4 OPENING

5 FIBER

D OUTER DIAMETER OF ELECTRIC FURNACE H HEIGHT OF ELECTRIC FURNACE

d OPENING DIAMETER OF ELECTRIC FURNACE

Claims (17)

1. An inorganic material having radiation resistance, the

inorganic material comprising SiO 2 , A1 2 0 3 , CaO, and Fe203 as

components,

wherein the mass percentages of the components in

terms of oxide in the inorganic material are as follows:

i) the total content of SiO 2 and A1 2 03 is from 40% by

mass to 70% by mass;

ii) the ratio A1 2 0 3 /(SiO 2 + A1 2 0 3 ) (mass ratio) is in

the range of 0.15 to 0.40;

iii) the content of Fe203 is from 16% by mass to 25%

by mass; and

iv) the content of CaO is from 5% by mass to 30% by

mass.

2. The inorganic material according to claim 1, wherein

the inorganic material is intended for a part to be

irradiated with radiation.

3. A fiber comprising the inorganic material according to

claim 1 or 2.

4. A fiber-reinforced composite material reinforced with

the fiber according to claim 3.

5. The fiber-reinforced composite material according to

claim 4, wherein the fiber-reinforced composite material is

a fiber-reinforced resin.

6. The fiber-reinforced composite material according to

claim 4, wherein the fiber-reinforced composite material is

a fiber-reinforced cement.

7. A method for producing an inorganic fiber having

radiation resistance,

the method comprising melt-spinning a mixture of a

silica source, an alumina source, a calcium oxide source,

and an iron oxide source,

wherein the mass percentages of SiO 2 , A1 2 0 3 , CaO, and

Fe203 in terms of oxide in the mixture are as follows:

i) the total content of SiO 2 and A1 2 03 is from 40% by

mass to 70% by mass;

ii) the ratio A1 2 0 3 /(SiO 2 + A1 2 0 3 ) (mass ratio) is in

the range of 0.15 to 0.40;

iii) the content of Fe203 is from 16% by mass to 25%

by mass; and

iv) the content of CaO is from 5% by mass to 30% by

mass.

8. The method for producing an inorganic fiber according to claim 7, wherein the inorganic fiber is used for a part to be irradiated with radiation.

9. The method for producing an inorganic fiber according

to claim 7 or 8, wherein fly ash is used as the silica

source or the alumina source.

10. The method for producing an inorganic fiber according

to claim 9, wherein the iron oxide source is copper slag.

11. The method for producing an inorganic fiber according

to claim 10, wherein the calcium oxide source is iron and

steel slag.

12. The method for producing an inorganic fiber according

to claim 7 or 8, wherein the silica source or the alumina

source is basalt or andesite.

13. The method for producing an inorganic material

according to claim 12, wherein the iron oxide source is

copper slag.

14. The method for producing an inorganic material

according to claim 13, wherein the calcium oxide source is

iron and steel slag.

15. Use of an inorganic material for a part to be

irradiated with radiation, the inorganic material including

SiO 2 , A1 2 0 3 , CaO, and Fe203 as components,

wherein the mass percentages of the components in

terms of oxide in the inorganic material are as follows:

i) the total content of SiO 2 and A1 2 03 is from 40% by

mass to 70% by mass;

ii) the ratio A1 2 0 3 /(SiO 2 + A1 2 0 3 ) (mass ratio) is in

the range of 0.15 to 0.40;

iii) the content of Fe203 is from 16% by mass to 25%

by mass; and

iv) the content of CaO is from 5% by mass to 30% by

mass.

16. The use of an inorganic material for a part to be

irradiated with radiation according to claim 15,

wherein the part to be irradiated with radiation is

any one of the following:

a) a nuclear reactor building, a nuclear reactor

containment vessel, piping inside a nuclear reactor

facility, and a decommissioning robot;

b) a space station building, a space station, an

artificial satellite, a planetary exploration satellite,

and a space suit; and c) medical devices utilizing particle beams.

17. A method for suppressing radiation-induced

deterioration of a fiber-reinforced composite material

constituting a part to be irradiated with radiation,

wherein an inorganic fiber including SiO 2 , A1 2 0 3 , CaO,

and Fe203 as components is used as the fiber, and

the mass percentages of the components in terms of

oxide in the inorganic material are as follows:

i) the total content of SiO 2 and A1 2 03 is from 40% by

mass to 70% by mass;

ii) the ratio A1 2 0 3 /(SiO 2 + A1 2 0 3 ) (mass ratio) is in

the range of 0.15 to 0.40;

iii) the content of Fe203 is from 16% by mass to 25%

by mass; and

iv) the content of CaO is from 5% by mass to 30% by

mass.

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